<!DOCTYPE html>
<html lang="ch">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>

        .box{
            width: 100%;
            height: 1500px;
            background-color: aqua;
        }

    .ad{
        width: 100px;
        height: 200px;
        background-color: red;
        /* 固定定位 相对于窗口 */
        position: fixed;
        right: 0;
        bottom: 100px;
    }

    </style>
</head>
<body>
    
    <div class="box"></div>


    <div class="ad"></div>
</body>
</html>